Electronic Medical System With Implantable Medical Device, Having Wireless Power Supply Transfer

ABSTRACT

An electronic medical system is described. The system comprises an external RF power transmitter configured to emit a first power signal via an electromagnetic coupling, said RF power transmitter being configured to emit said first energy signal with a power no greater than 1W. The system further comprises an implantable medical device comprising: at least one receiver antenna configured to receive said first energy signal via an electromagnetic coupling; an RF power receiver module configured to extract a second energy signal having a power of at least 1 mW and to be powered by said second energy signal; a power actuator module, operatively connected to the RF power receiver module, powered by said second energy signal. The power actuator module is configured to deliver a medical treatment to at least a target tissue of a patient on the basis of a control signal generated by the RF power receiver module.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to the field of human bodymedical treatment system with implantable medical devices, particularly,to an electronic medical system with implantable medical device, havingwireless power supply transfer.

BACKGROUND

In recent years, medical treatment of the human body (e.g. electricalstimulation of various tissues or organs, delivering of medicalsubstances into tissues or organs, and so on) has been increasingly usedto treat a number of different medical conditions such as for examplechronic pain disorder, alcohol and drug dependence, and otherpathological conditions.

In the case of electrical stimulation, while a few of these treatmentsare applied by using external devices and electrodes, the majority andthe most relevant of these techniques involves implanting electrodes andoften the entire stimulating device in the human body.

Several commercial implantable devices have been manufactured andsuccessfully applied and they are becoming increasingly adopted.

A typical electronic medical system for electrical stimulation includesan implantable medical device having one or more electrodes deliveringelectrical stimulus to a specific tissue or organ in the form of anelectrical current or voltage signals.

Furthermore, the implantable medical device includes a control unit thatis configured to modulate and provide an appropriate sequence of stimuli(typically, a periodic sequence of electrical voltage or currentimpulses), wherein the frequency, duty cycle and amplitude of theelectrical signal can be adaptively varied in order to maximize theeffectiveness of the treatment for each individual patient.

In addition, the implantable medical device typically includes aconductive element (e.g. a catheter) connecting the control unit to theelectrodes, and an energy storage element providing the power supply tothe control unit, usually in the form of an electro-chemical storagedevice, or a battery.

The electronic medical system having said implantable medical device hasseveral limitations.

First of all, the control unit and energy storage element (battery) areusually integrated and occupy a relatively sizeable volume. Furthermore,both the control unit and the battery need to be suitably protected byinserting them into a rigid metallic case coated in biocompatiblematerials, and then implanted in a suitable anatomical cavity, in mostcases disposed relatively far away from the tissue or the organ to bemedically treated (e.g. electrically stimulated).

For this reason, a routing of a relatively long catheter from thecontrol unit to the electrodes, thus increasing post-surgery patientdiscomfort and the probability of infections, is needed.

Moreover, the implantation of the medical treatment system typicallyrequires at least two different surgeries on the patient.

In a first surgery, the electrodes are accurately placed in the targetposition (tissue or organ) into the human body, while the control unitand the battery are kept external and are connected to one anotherthrough a catheter. This is required to test the patient's reaction tothe medical treatment procedure and eventually to adjust, to optimizeand to fine tune the parameters of the electrical stimulus. Once theeffectiveness of the medical treatment procedure has been tested, asecond surgery is performed on the patient to implant the control unitin the target location. Obviously, performing two subsequent surgeriesrepresents a inconvenience for the patient.

Furthermore, a number of disadvantages arise from the presence of anelectrochemical energy storage element (battery), e.g. the limitedbattery's lifetime which implies the need of its replacement by surgery,the impossibility of performing Magnetic Resonant Imaging (MRI) test,the presence of heavy metals and other potentially hazardous material,such as mercury, cadmium, nickel, and lithium, requiring extra care fordisposal avoiding leakage.

SUMMARY OF THE INVENTION

According to some aspects of the present description, an electronicmedical system with wireless power supply transfer is provided whichovercomes the drawbacks above mentioned with reference to the citedprior art.

According to a first embodiment, there is provided a electronic medicalsystem comprises an external RF power transmitter configured to emit afirst power signal via an electromagnetic coupling, said RF powertransmitter being configured to emit said first energy signal with apower no greater than 1 W. The system further comprises an implantablemedical device comprising: at least one receiver antenna configured toreceive said first energy signal via an electromagnetic coupling; an RFpower receiver module operatively connected to the at least one receiverantenna, the RF power module being configured to extract a second energysignal having a power of at least 1 mW, the RF power receiver modulebeing powered by said second energy signal, the RF power receiver modulebeing configured to generate a control signal; a power actuator module,operatively connected to the RF power receiver module, powered by saidsecond energy signal, the power actuator module being configured toreceive said control signal, the power actuator module being configuredto deliver a medical treatment to at least a target tissue of a patienton the basis of said control signal.

Further aspects are provided in the description, drawings and claims ofthe present application.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the system according to the presentdisclosure will appear more clearly from the following description ofpreferred embodiments thereof, given by way of a non-limiting examplewith reference to the annexed figures, wherein:

FIG. 1 shows a block diagram of a medical treatment system with wirelesspower supply transfer according to an embodiment of the disclosure;

FIG. 2 shows a block diagram of a first portion of the system of FIG. 1;

FIG. 3 shows a block diagram of a component of the first portion of thesystem of FIG. 2;

FIG. 4 shows with an electric circuit the component of FIG. 3 accordingto an embodiment of present disclosure;

FIG. 5 shows with a block diagram a second portion of the system of FIG.1;

FIG. 6 shows with a block diagram a component of the second portion ofthe system of FIG. 5;

FIG. 7 shows with an electric circuit the second portion of FIG. 5according to an embodiment of the present disclosure;

FIGS. 8, 9, 10 and 11 illustrates with diagrams waveforms obtained withsimulations performed on the electric circuit of FIG. 7;

FIG. 12 shows with an electric circuit the first portion of FIG. 5according to a further embodiment of the present disclosure;

FIG. 13 illustrates a block diagram of a further component of the secondportion of the system of FIG. 5;

FIGS. 14 a-14 b illustrate a cross section view and a top view,respectively, of an arrangement of a component of the system of thepresent disclosure on a portion of a target tissue, according to anembodiment of the present disclosure;

FIGS. 15, 16 and 17 illustrate top views of arrangements of componentsof the system of the present disclosure on a portion of a target tissue,in accordance with different embodiments of the present disclosure,respectively;

FIG. 18 illustrates an electric circuit of the first portion of thesystem of FIG. 2, according to a further embodiment of the presentdisclosure;

FIG. 19 illustrates an electric circuit of the second portion of thesystem of FIG. 5, according to a further embodiment of the presentdisclosure;

FIG. 20 illustrates an electric circuit of the second portion of thesystem of FIG. 5, according to a further embodiment of the presentdisclosure;

FIG. 21 illustrates with an electric circuit a representation of thesystem of the present disclosure, and

FIGS. 22, 23, 24 and 25 illustrate with diagrams waveforms obtained withsimulations performed on the system of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the block diagram of FIG. 1, an electronic medicalsystem 100 with wireless power supply transfer, hereinafter alsoreferred to simply as system 100, is now described.

The system 100 comprises an external RF (Radio Frequency) powertransmitter 101 configured to communicate and transfer RF energy via awireless transfer, i.e. an electromagnetic coupling in the far fieldregion.

The external RF power transmitter 101 may be worn by or carried by apatient as a portable device or may be positioned near the patient.

In greater detail, the external RF power transmitter 101 is configuredto emit a first energy signal S1 via an electromagnetic coupling. Inorder to meet regulatory and safety constraints, the external RF powertransmitter 101 is advantageously configured to emit said first energysignal S1 having an instantaneous transmission power no greater than 1 W(30 dBm).

It should be observed that the above indicated value of 1 W correspondsto a value of Equivalent Isotropic Radiated Power (EIRP) of 30 dBm.

With reference again to FIG. 1, the system 100 further comprises animplantable medical device 102, configured to receive from the externalRF power transmitter module 101 said first energy signal S1. As it willbe described later, the implantable medical device 102 may be implantedunder the skin of the patient.

With reference now to FIG. 1 and FIG. 2, the external RF powertransmitter 101, hereinafter also simply transmitter 101, comprises a RFpower transmitter module 200.

The transmitter 101 further comprises an energy storage element 201,e.g. a battery or a rechargeable battery, operatively connected to theRF power transmitter module 200. The energy storage element 201 isconfigured to transmit power to the RF power transmitter module 200 andgenerally to the transmitter 101.

In addition, the transmitter 101 comprises a power limiter module 202operatively connected to the RF power transmitter module 200. The powerlimiter module 202 is configured to limit the first energy signal S1 toan instantaneous transmission power no greater than 1 W.

It should be noted that the power limiter module 202 can be implementedin various way. An example of power limiter module 202 will be providedin the following.

The transmitter 101 further comprises a first communication interfacemodule 203 operatively connected to the RF power transmitter module 200.

The first communication interface module 203 is configured tocommunicate data (transmit and receive) with the implantable medicaldevice 102 via a wireless link (forward and reverse link), as it will bealso explained later. The first communication interface module 203comprising a coder and a decoder of the communication data, a modulatorand other elements configured to performs the functions required toexchange data via the forward and the reverse link between thetransmitter 101 and the implantable medical device 102. The firstcommunication interface module is configured to operate with a low powerwireless communication protocol such as, for example, Bluetooth 4.0, ANTand/or ANT+, Zigbee, and so on.

The transmitter 101 further comprises a first programmable control unit204, i.e. a microprocessor or a microcontroller, configured to managethe transmitter 101. In fact, the first programmable control unit 204 isoperatively connected to all the components of the transmitter 101.

With reference now to the block diagram of FIG. 3, the RF powertransmitter module 200 is now described.

The RF power transmitter module 200 comprises an RF power amplifier 301,an impedance matching module 302, a resonant network module 303 and atransmitter antenna 304 in cascade arrangement. Such an arrangement isconfigured to receive an input power IP from the battery 201 and togenerate the first energy signal S1 having an instantaneous transmissionpower no greater than 1 W, to be emitted via the electromagneticcoupling to the implantable medical device 102, at a carrier frequencycomponent preferably of 433.92 MHz.

In a greater detail, the RF power amplifier 301 is configured togenerate an RF output signal with the required power level from a lowpower input, the impedance matching module 302 is configured to maximizethe power to be transferred to the transmitter antenna 304, i.e. tominimize reflections of power into the RF power amplifier 301), theresonant network module 303 is configured to maximize the circuit Q,i.e. to increase the power to be transferred at the dominant frequencyof operation with respect to the nearby frequencies (i.e. narrow-band).

With reference to FIG. 4, the transmitter 101 is represented by acircuital point of view in accordance with an embodiment of the presentdisclosure.

It should be noted that the electric component corresponding to theblocks of FIG. 2 or 3 are indicated with the same reference numbers orthey are grouped within blocks with dotted lines indicated with the samereference numbers.

According to an embodiment of the present disclosure, the RF poweramplifier 301 is a Class-E amplifier with Zero Voltage Switching. Itshould be noted that a Class-E amplifier, operating in soft switching,advantageously allows to guarantee high efficiency (ideally close to100%) and low distortion.

According to another embodiment, the RF power amplifier 301 isconfigured to generate a second (H2) and a third (H3) harmoniccomponents that are at least 70 dBc less than the carrier frequencycomponent (433.92 MHz).

With reference now to FIG. 1 and FIG. 5, the implantable medical device102 comprises at least one receiver antenna 501 configured to receivesaid first energy signal S1 via an electromagnetic coupling, i.e. in thefar field region.

The at least one receiver antenna 501 may be of the subcutaneous type.

In particular, the at least one subcutaneous antenna 504 can be placedon the target tissue or buried in the target tissue in order to minimizelosses in the radiated signal, i.e. the first energy signal S1.

With reference to FIGS. 14 a and 14 b, the target tissue 10 comprises askin layer 11 and a fat layer 12 (shown only in FIG. 14 a). Thetransmitter antenna 304 of the external RF power transmitter 101 isarranged in proximity of the target tissue 10, above the skin layer 11.

As illustrated in the FIG. 14 b, the transmitter antenna 304 of theexternal RF power transmitter 101 can be a metal folded dipole. In thesame way, in an embodiment of the present disclosure, also the at leastone subcutaneous antenna 501 may be a metal folded dipole.

According to the embodiment of FIG. 15, the at least one subcutaneousreceiver antenna 504 may be placed in the skin layer 11, e.g.immediately under the skin layer 11, of the target tissue 10. The atleast one subcutaneous receiver antenna 504 is placed at a distance dfrom the transmitter antenna 304, e.g. at a frequency of 433.92 MHz.

According to the embodiment of FIG. 16, the at least one subcutaneousreceiver antenna 504 may be placed in the fat layer 12 of the targettissue 10. The at least one subcutaneous receiver antenna 504 is placedat a distance d from the transmitter antenna 304, e.g. at a frequency of433.92 MHz. It should be observed that the lower conductivity of the fatlayer 12 of the target tissue 10 allows to obtain losses lower thanplacing the at least one subcutaneous receiver antenna 501. Therefore,it is preferable to bury the at least one subcutaneous receiver antenna501 in the fat layer 12 of the target tissue 10.

According to the embodiment of FIG. 17, the at least one subcutaneousreceiver antenna 504 may be buried in the fat layer 12 of the targettissue 10. The at least one subcutaneous receiver antenna 504 is placedat a distance d from the transmitter antenna 304, e.g. at a frequency of433.92 MHz. In this embodiment, the at least one subcutaneous receiverantenna 504 is coated in a bio-compatible material 13, e.g. silicone.Embedding the at least one subcutaneous receiver antenna 504 in thebio-compatible material advantageously improves the gain of the antenna.

According to an embodiment of the present disclosure, the bio-compatiblematerial 13 can be a low electrical conductivity material, typicallyless than 10⁻¹⁰ S/m (e.g. glass is 10⁻¹¹ S/m, rubber or plastic is 10⁻¹⁴S/M or lower—10⁻²⁰ S/m), e.g. a polymer.

According to another embodiment, further improvement in the antenna gaincan be achieved by using a secondary metallic strip coupled to the atleast one subcutaneous receiver antenna 504 to maximize the gain in thedirection of the metal strip or in the opposite direction depending onthe length of the structure. This technique improves the antenna gain of˜3 dB increasing further the range.

In addition, in order to provide enough power at the RF power receivermodule 502 for the system 100 to work properly, it is necessary to havethe transmitter antenna 304 and the at least one subcutaneous receiverantenna 504 separated less than 30-35 cm. This can be valid specificallywhen using a directional antenna at the RF receiver power module.

In addition, it should be noted that also since any object that will beplaced between the transmitter antenna 304 and the at least onesubcutaneous receiver antenna 504 will negatively impact the path loss aclear line of sight is required between the two antennas.

According to another embodiment, in combination with any of the previousembodiment, the at least one subcutaneous antenna is printed on aflexible material, e.g. a conductive polymer antenna printed on plasticfilms.

Furthermore, according to another embodiment, in combination with any ofthe previous embodiment, the at least one subcutaneous receiver antenna501 is an omnidirectional antenna.

According to an alternative embodiment, the at least one subcutaneousreceiver antenna 501 is a directional antenna.

According to other embodiments, alternatively or in combination with thepreviously described embodiments, the at least one receiver antenna 104may be a dipole antenna, a monopole antenna, a slot antenna, a patchantenna, or an antenna with another form factor configured to receivethe first energy signal S1 via the electromagnetic coupling in the farfield region.

With reference to the distance d between the transmitter antenna 304 andthe at least one subcutaneous receiver antenna 504, to ensure the powertransfer necessary for the implantable medical device 102 to workproperly without battery, the loss introduced by the wireless linkbetween the transmitter antenna 304 and the at least one subcutaneousreceiver antenna 504 needs to be less than 25 dB.

If both the above indicated antennas are placed in the far field region,the ratio of the power received (Pr) over the power transmitted (Pt) canbe estimated using the following equation:

Pt/Pr[dB]=Gt[dB]+Gr[dB]+20 log 10[λ/4πd]

wherein Gt and Gr are the gain of the transmitter antenna 304 and the atleast one subcutaneous receiver antenna 504, respectively; A is thewavelength in the free space and d is the distance between the aboveindicate antennas.

The higher the antenna gain at the RF power receiver module 502 and atthe transmitter module 101 and the higher the maximum distance for whichthe communication/power transfer system performs properly, e.g. when theratio Pr/Pt>−25 dB.

The requirement for having the system working for distance, d, greaterthan 20 cm determines to have the system operating at frequencies, f, inthe ISM bands below 2 GHz. Considering also that the human tissue thatsurrounds the at least one subcutaneous receiver antenna 504 has astrong negative effect on Gr, in the order of ˜15 dB of loss, it isproposed to adopt a frequency of operation below 500 MHz. For thisreason, the selected frequency for the system can be 433.92 MHz (thehighest frequency of the regulated ISM frequencies below 500 MHz),already previously introduced. It should be noted that the highestpossible frequency below 500 MHz has been selected to advantageouslyallow the design of small antennas and small components of the system100.

The path loss of the wireless link has been determined throughelectromagnetic simulations to determine the maximum distance at whichthe transmitter antenna 304 and the at least one subcutaneous receiverantenna 504 need to be placed. To this end the electromagneticsimulations have been conducted modeling the tissues of the head (targettissue) as a two layers material composed of a first layer of skin and asecond layer of fat, as previously defined.

With reference again to FIG. 5, the implantable medical device 102further comprises a RF power receiver module 502 operatively connectedto the at least one receiver antenna 501.

The RF power receiver module 502 is configured to extract a secondenergy signal S2 having an instantaneous power of at least 1 mW, on thebasis of said first energy signal S1.

In addition, the RF power receiver module 502 is configured to generatea control signal CS.

The implantable medical device 102 further comprises a power actuatormodule 503, operatively connected to the RF power receiver module 502,configured to receive said control signal CS.

In particular, the power actuator module 503 is configured to deliver amedical treatment to at least a target tissue of a patient on the basisof said control signal CS.

It should be noted that, according to a first embodiment of the presentdisclosure, the medical treatment is an electronic stimulation of thetarget tissue. In such first embodiment, the power actuator module 503may include a pulse signal generator configured to apply electricalstimulation to the target tissue, controlled by means of the controlsignal CS, providing electrical stimuli to one or more electrodesoperatively connected to the target tissue.

In particular, the one or more electrodes may be configured to bepositioned in proximity to, or attached to, the target tissue of thepatient to provide electrical stimulation to the target tissue. The oneor more electrodes may be coupled directly to the implantable medicaldevice 102 (i.e. without leads) or may be coupled to the implantablemedical device 102 via one or more leads.

According to a second embodiment, alternative to the first one, themedical treatment is the action of a medical substance (drug), e.g.insulin. In such second embodiment, the power actuator module 503 may bea pump, controlled by means of the control signal CS, to dispense themedical substance into the target tissue.

In a first embodiment, the substance may be liquid, e.g. insulin.

According to a second embodiment, the substance may be solid, e.g.insulin.

With reference again to the power actuator module 503, according toanother embodiment, it can be configured to move a fluid solution from areservoir into the target tissue of the patient. In particular, in suchan embodiment, the target tissue can be an organ of the patient.

The target tissue may include neural tissue (e.g. one or more areas ofthe brain, the spinal cord, a cranial nerve, or another nerve), a vagusnerve, a trigeminal nerve, a glossopharyngeal nerve, a hypoglossalnerve, muscular tissue (e.g. a heart muscle), or another nerve ortissue.

With reference again to the block diagram of FIG. 5, the implantablemedical device 102 further comprises a second communication interfacemodule 504 operatively connected to the RF power receiver module 502.The second communication interface module 504 is configured tocommunicate data (transmit and receive) with the external RF powertransmitter 101 via a wireless link (forward and reverse link), as itwill be also explained later. The second communication interface module504 comprising a coder and a decoder of the communication data, amodulator and other elements configured to performs the functionsrequired to exchange communication data via the forward and the reverselink between the transmitter 101 and the implantable medical device 102.The second communication interface module is configured to operate witha low power wireless communication protocol such as, for example,Bluetooth 4.0, ANT and/or ANT+, Zigbee, and so on.

The implantable medical device 102 further comprises a secondprogrammable control unit 505, e.g. a microprocessor or amicrocontroller, operatively connected to the RF power receiver module502, configured to manage the implantable medical device 102. In fact,the second programmable control unit 505 is operatively connected to allthe components of the implantable medical device 102.

The implantable medical device 102 further comprises a reference module506 operatively connected to both the RF power receiver module 502 andthe second programmable control unit 505. The reference module 506 isconfigured to generate reference current or voltage values used inseveral functions performed during the operation of the implantablemedical device 102, e.g. to generate accurate reference current orvoltage values in the case the device delivers current of voltagestimuli.

In particular, the reference module 506 is configured to generate areference voltage used by a pulse generator module (described later)within the RF power receiver module 502.

In addition, the implantable medical device 102 further comprises anAnalog-to-Digital Converter (ADC) module 507 operatively connected toboth the RF power receiver module 502 and the second programmablecontrol unit 505. In particular, the ADC module 507 is configured toreceive from the target tissue an analog value representative of thetarget tissue impedance (resistance) and to convert it into a digitalvalue representative of the target tissue impedance, to be sent to thetransmitter 101 as a feedback value.

With reference now to both FIG. 5 and FIG. 6, the RF power receivermodule 502 comprises a RF front end module 601 configured to receivefrom the receiver antenna 501 the first energy signal S1. The RF frontend is configured to generate a rectified voltage level VL to beprovided to a voltage rectifier, subsequently described, by means of ahigh Q (Quality) resonant circuit (not shown in the FIG. 6).

The RF power receiver module 102 further comprises an impedance matchingnetwork 602 operatively connected to the at least one receiver antenna501 via the RF front end module 601.

The impedance matching network 602 is configured to match the impedanceof the at least one receiver antenna 501 to the other components of theimplantable medical device 102 to achieve high efficiency powertransfer. For example, the resistance of the antenna may be relativelylow, e.g. on the order of a few Ω up to 50Ω, and one or more othercomponents of the implantable medical device 102 may have acomparatively high resistance, e.g. on the order of KΩ). The impedancematching network 601 may facilitate impedance matching from therelatively low resistance of the at least one receiver antenna 501 to arelatively high resistance of some components of the implantable medicaldevice 102.

It should be observed that the radiated power reaching the at least onereceiver antenna 501 is limited and depends on the transmitted power,the distance between the external RF power transmitter 101 and theimplantable medical device 102, the loss tangent of the target tissue.The efficiency at the maximum power transfer conditions is not higherthan 50%. The impedance of the at least one receiver antenna 501 canvary depending on the presence or not of object in the wireless linkbetween the external RF power transmitter module 101 and the implantablemedical device 102, the conductivity of the target tissue around the atleast one receiver antenna 501 and other parameters. Therefore, theimpedance matching network 602 may be preferably of the tunable type.

The RF power receiver module 502 further comprises at least one voltagerectifier 603 operatively connected to the impedance matching network602. The at least one voltage rectifier 603 is configured to rectify thefirst energy signal S1 received by the at least one receiver antenna 501to generate a rectified voltage signal VO, on the basis of the rectifiedvoltage level VL.

The RF power receiver module 502 further comprises the power actuatormodule 503 (previously described) operatively connected to the voltagerectifier module 603 to receive from it the necessary power to operate.

According to first embodiment, previously introduced, the power actuatormodule may be a pulse generator configured to provide electricalstimulation on the target tissue via one or more electrodes (not shownin FIG. 6) placed on or in proximity of the target tissue.

According to a second embodiment, previously introduced, the poweractuator module may be a pump configured to dispense a medical substance(drug) to the target tissue.

With reference again to the block diagram of FIG. 6, the RF powerreceiver module 502 further comprises a voltage protection andbackscattering module 604 operatively connected to the at least onereceiver antenna 501 via the RF front end module 601.

In addition the voltage protection and backscattering module 604 isoperatively connected to all the other modules of the RF power receivermodule 502.

Furthermore, the voltage protection and backscattering module 604 isoperatively connected to the target tissue (not shown in FIG. 6).

The voltage protection and backscattering module 604 is configured totransmit to the external RF power transmitter 101 feedback informationreceived from the target tissue.

Feedback information comprises patient feedback information, i.e.measured target tissue parameter, typically voltages and conductivity(e.g. impedance), measured patient's vital parameter, e.g. heart rate,and/or medical treatment information, i.e. treatment deliverysuccess/fail information.

It should be observed that the external RF power transmitter module 101is advantageously configured to control, i.e. stop, pause or restart,the RF power transmission on the basis of said feedback informationreceived from the implantable medical device 102.

In fact, the first programmable control unit 204 of the external RFpower transmitter 101 is configured to control, i.e. stop, pause orrestart, the RF power transmission, on the basis of said feedbackinformation.

In addition, the external RF power transmitter 101 is configured todetect the feedback information in order to communicate, back to thetransmitter 101, tissue impedance values for clinical purposes, inaddition to the fact that, in order to make sure that the energy at theRF power receiver module 502 is high enough to actuate the neuralstimulation, a feedback of successful operation to the transmitter isgenerally desirable.

Furthermore, in the case exceeding energy is transferred to the RF powerreceiver module 502, rather than wasting energy by partially cloakingthe RF power receiver module 502, the level of transmitted power couldbe lowered in order to save battery energy.

If the external RF power transmitter 101 is configured to detect theshunting of the at least one receiver antenna 504, the transmitted powercould be reduced, otherwise the operation of the receiver output voltageprotection could be transmitted back to the transmitter bybackscattering modulation.

With reference to FIG. 7, the implantable medical device 102 isrepresented by a circuital point of view in accordance with anembodiment of the present disclosure.

A first resistor R9 and a first inductance L8 represent the antennaimpedance at the frequency of 433.92 MHz.

A first capacitor C6, a second capacitor C7, a second inductance L6, athird capacitor C8 and a third inductance L7 represent the tunableimpedance matching network 602. All the resistors in this impedancematching network are parasitic components. By making the secondcapacitor C7 and the third capacitor C8 as variable capacitors, theimpedance matching network can be tuned to match the load to the antennaimpedance for various values of antenna impedance. This is possibleassuming to have enough power stored or received to enable the tuning ofthe capacitors. If the RF power receiver module 502 is totally detuned,no power may be received to enable the tuning of the impedance matchingnetwork resulting in failure. Therefore, it is very important to set thedefault values of the tuning capacitors such a reasonable amount ofenergy is transferred to start up the circuit of the RF power receivermodule 502.

With reference again to the electric circuit of FIG. 7, a first diode D1and a second diode D2 represent the voltage rectifier 603 configured totransform the first energy signal S1 (AC RF signal) into a DC referencevoltage VO. The forward voltage and the parasitic capacitance of thefirst diode D1 and the second diode D2 guarantee high efficiency for thecircuit.

A fourth capacitor C9 is the output filter capacitor and represents theelement able to charge/discharge the energy needed to power the poweractuator module.

A second resistor R15 represents the continuous load, i.e. the poweractuator module.

With reference to FIG. 8, main simulated waveforms of the RF powerreceiver module 502 as represented by the electric circuit of FIG. 7 arerepresented, in the case the output filter capacitor C9 has a value of100 pF.

In particular, the first (upper) waveform is the voltage of the anode ofthe second diode D2, the second (in the center) waveform is the outputvoltage (node OUT) and the third (lower) waveform is the voltage at thenode named as A.

With reference to FIG. 9, dynamic powers for the same simulation arerepresented.

In particular, the input power (upper waveform) is limited to about 2 mW(power units are indicated in mV but they should be indicated in mW) andthe output power (lower waveform) is in excess of 1 mW.

It can be also noted that the efficiency (center waveforms), alsoindicated as V in the diagram but computed directly as percentage) afterthe initial peak around 60%, is settled at values slightly in excess of50%.

The antenna impedance may vary depending on the operating conditions.

In particular, with reference to FIG. 10, it has been verified that forvalues of the first resistor R9 (real part) between 0.1Ω and 10Ω withthe imaginary part between 13.5Ω and 82Ω, the impedance matching network602 can be tuned to guarantee an efficiency in the order of 50% with aload (second resistor R15) of 25 KO.

With reference to FIG. 8, the implantable medical device 102 ispresented by a circuital point of view in accordance with a furtherembodiment of the present disclosure.

It should be observed that when the reactive part of the antennaimpedance changes, rather than tuning the first capacitor C6 to maintainthe resonance, it is preferable to tune the second capacitor C7 tore-adjust the impedance and bring back the desired efficiency.

However, the first capacitor C6 is important to guarantee high enoughvoltage level at the output by de-coupling the antenna impedance fromthe rest of the electric circuit of FIG. 7.

Furthermore, the first capacitor C6 could be considered part of the atleast one receiver antenna 501 if its impedance becomes capacitive(negative reactance) and it will allow the desired performance for thereceiver also in that case.

The impedance that the electric circuit sees looking into the voltagerectifier 603 is quite high both in its real part and in its imaginarypart. The real part can be estimated to be close to 100Ω and itsimaginary is positive and can be estimated to be around 400Ω. Theimpedance matching network 602 of the RF power receiver module 502 isvery flexible.

Turning back to the load, as mentioned above, the load is typically theoutput filter capacitor C9 (fourth capacitor C9) until it gets chargedto the desired voltage (e.g. 5V) for neural pulse discharge duringneural stimulation, in the case the power actuator module is directed toperform electronic stimulation.

Therefore, it has been verified that the efficiency remains high formuch of the charging time without any specific resistive load.

With reference now to FIG. 11, simulated waveforms are showncorresponding to the electric circuit of Fi. 7 but without the loadresistor of 25 KΩ and with the output filter capacitor C9 of 5 nF.

It can be noticed that during the charge of the output filter capacitorC9, between 1 V and 5 V of values of the output voltage, the efficiencyremains high (with peaks in excess of 60%) which is desirable.Initially, there is a dip of the output power, but that is notcorresponding to reality because it is due to the low pass filtering ofthe output power. The simulation illustrated in FIG. 11 has beenperformed with a real part of the antenna impedance of 1Ω. It is clearthat if the resistive part of the at least one receiver antenna 501 ishigher the efficiency values are lower for lower output voltages, andthus the time it takes to charge the output filter capacitor is longer.It has been verified that for antenna equivalent resistance of 70Ω thetime would be about twice as long. The RF power receiver module 502 isanyway sized so that the efficiency is higher for values of outputvoltage around 4-5 V.

Returning back to the RF power receiver module 502, it should beobserved that one of its important aspects is the ability to operatewithout injecting harmonics in the antenna current. The presence of thevoltage rectifier, being a non-linear circuit, inherently introducesharmonics with significant amplitude in the current. These harmonics arevery undesirable because they get transmitted back from the at least onereceiver antenna 501 and could be disturbing other circuits and RFcommunication links. In particular, the most difficult harmonicfrequency to suppress is the third one (having a frequency of 1.3 GHz).

By forcing the output voltage to be around 5 V, the impedance ofelectric circuit of FIG. 7 does not change with the output voltage andthe electric circuit can be simulated with an input power of 2 mW(without power limiting voltage source, but with simplified behavioralmutually coupled transmitter circuit) to analyze the spectrum of theantenna current.

In particular, it has been observed that the third harmonic frequency isquite high (about 45 dB below the carrier frequency).

Therefore, it needs to be filtered of anyway attenuated at least 60 dBbelow the fundamental harmonic frequency.

In order to obtain that, with reference to the electric circuit of FIG.12, a first order resonant filter L9, C10 has been placed on the left ofthe second diode D2. The first order resonant filter L9, R10 is resonantat the third harmonic frequency and the impedance of the parallelcircuit is very high at that frequency. The first order resonant filterL9, C10 introduces a minor attenuation but it is within acceptablelevels.

With reference now to FIG. 13, a power actuator module 503, according tothe embodiment wherein it is configured to perform electronicstimulation of the target tissue, is now described. In other words, inFIG. 3, the power actuator module 503 is an electronic pulse generator,i.e. a neural pulse generator.

The power actuator module 53 comprises a current regulator 701 from theoutput voltage Vout to a lead LD to the one or more electrodes (notshown in the FIG. 13). The current regulator 701 is connected to thelead LD via a first switch S1. The current regulator 701 may be acurrent mirror.

In addition, the power actuator module 503 further comprises a voltageregulator 702 from the output voltage Vout to the lead LD to the one ormore electrodes. The voltage regulator 702 is connected to the lead LDvia a second switch S2.

The voltage regulator 701 can be implemented with a LDO (Low Drop-Out)regulator. In alternative, a buck switching power converter could beused. As a third alternative, if the output capacitor Cout filtering theoutput voltage Vout is large enough to not drop its voltagesignificantly during the electronic stimulation (e.g. neuralstimulation), the output voltage could be directly regulated to be at apreset therapy voltage (e.g. 3.6 V) rather than 5 V.

The power actuator module 503 further comprises a Voltage and CurrentMode Selection module 703 configured to control both the first switch S1and the second switch S2.

In particular, the Voltage and Current Mode Selection module 703 isconfigured to select the electronic stimulation mode by opening/closingthe first switch S1 and closing/opening the second switch S2,respectively.

According to the embodiment of FIG. 13, the power actuator module 503further comprises a comparator module 704, i.e. an operationalamplifier, configured to compare the output voltage Vout with aprogrammable voltage reference 705. The output of the comparator module705 is operatively connected to the lead LD to the one or moreelectrodes via a third switch S3. In particular, the comparator module704 is configured to control the third switch Se (opening/closing) onthe basis of the result of the comparison of the output voltage Vout andthe programmable reference voltage output 705.

It should be observed that the programmable reference voltage output 705should be set such that knowing the value of the output capacitor Coutand its regulated voltage, the timing of the pulse could be determinedby computing the voltage drop on the output capacitor Cout during thepulse. The comparator module 704 is configured to open (turn off) thethird switch S3 when the programmable reference output voltage(threshold) has been reached.

Alternatively, an analog or digital timer should be designed todetermine the duration of the pulse.

According to an alternative embodiment, the output of the comparatormodule 705 could be directly connected to the Voltage and Current ModeSelection module 703 in order to directly control the opening/closing ofthe first switch S1 and the second switch S2.

With reference now to the electric circuit of FIG. 18, the external RFpower transmitter 101 of the system 100 is represented by a circuitalpoint of view in accordance with another embodiment of the presentdisclosure.

With reference to the previous embodiment illustrated in FIG. 4, thetransmitter 101 of FIG. 18 comprises a further filter represented by theresistors R16 and R17 with the capacitor C11. A backscattering filteredsignal (feedback information, as previously described) is detected atthe node B of the circuit.

As an example, the reverse link communication can be implement as ASKmodulation between two levels of amplitude. The modulation depth shouldbe quite high in order to guarantee reception of the signal and thisprevents the charge of the receiver capacitor (effective transfer ofenergy) during reverse link communication.

With reference now to the electric circuit of FIG. 19, the implantablemedical device 102 is represented by a circuital point of view inaccordance with another embodiment of the present disclosure.

The RF power receiver module 502 comprises a ASK demodulator typicallyimplemented as an AC coupled envelope detector coupled to the output ofthe impedance matching network.

The ASK modulation detector is basically an envelope detector AC coupledto the node A of the RF receiver power module. It is very important thatthis circuit does not attenuate significantly the main signal in ordernot to degrade the efficiency of the system 100. The power consumed bythe ASK demodulator and other coupled blocks has to be minimum andnegligible with respect to the desired output power.

The transistor MN2 is used for the backscattering modulation for reverselink communication. The transistor MN2, when turned on and off at agiven frequency, shunts the antenna thus altering its impedance and thisvariation is reflected back to the transmitter 101.

With reference now to the electric circuit of FIG. 20, the implantablemedical device 102 is represented by a circuital point of view inaccordance with another embodiment of the present disclosure.

Although the RF power receiver module 502 can be designed to have thehighest efficiency when its output voltage is between 4 V and 5 V, whenthe RF receiver power module 502 has no continuous load (only the outputcapacitor C9 as a load), the output power does not drop for voltageshigher than 5V, because the open load output voltage is much higher than5V.

However the output voltage could and should be limited, and thereforethe components of the RF power receiver module 502 needs to be protectedfrom over-voltages by the use of a linear regulation circuit. In fact, alinear regulation guarantees constant output voltage without introducingundesired harmonics at the at least one subcutaneous receiver antenna.

As illustrated in FIG. 20, a simple Operational TransconductanceAmplifier (OTA), a voltage reference with an output filter configured todrive the transistor MN2 shunting the antenna can regulate the outputvoltage out at the desired voltage.

Of course, given the small power values, it would be simpler andinexpensive to use a Zener diode at the output for protection purposes,but the shunt transistor is the same one that can be used forbackscattering modulation as well, as long as it is driven fully on orfully off when communicating in reverse link. The proposed circuit ismore accurate and even though a Zener diode would consume no currentuntil it is forward biased, the proposed circuit can be made veryefficient.

The controlled voltage source B5 represents a behavioral comparator tocompare the reference (ideal voltage source V3) with the output voltage,the further resistor R20 represents the transconductor and the furthercapacitor C14 along with the series resistor R19 defines the pole-zerofilter of the OTA. The further diode D5 is a simple clamp to preventlarge negative voltages at the gate terminal of the transistor MN2.

It should be noted that the entire system 100 has been simulated tobetter emulate the final system and in particular to understand theinteractions between the external RF power transmitter module 101(transmitter) and the implantable medical device 102 (receiver).

In order to simulate the system 100, it has been decided to utilizemutually coupled inductances to analyze the interaction between thetransmitter and receiver module. Typically this is more appropriate forinductive coupling and/or near field wireless power transfer types,however the main phenomena are quite similar provided that the propercoupling coefficient between the two coupled inductances is used. Thecoupled inductances are the inductive part of the antennas, providedthat their impedance at the selected frequency has an inductivecomponent.

The coupling coefficient can be determined using the electric circuitrepresented in FIG. 21.

In this specific case the two coupled inductances are equal in value,but since the antenna impedance varies, the change in the couplingcoefficient, if one or both inductances change, has to be taken intoaccount.

By developing the equations for the electric circuit of FIG. 21, it canbe obtained:

$\eta = {\frac{P_{load}}{P_{V\; 1}} = \frac{\omega^{2}M^{2}R_{L}}{\left( {R_{r} + R_{L}} \right)\left\lbrack {{R_{t}\left( {R_{r} + R_{L}} \right)} + {\omega^{2}M^{2}}} \right\rbrack}}$

therefore the efficiency, from the source, at the transmitter side, allthe way to the load, is defined as a function of the resistors, of thefrequency and of M (mutual inductance).M=k√{square root over (L₁L₂)} (or M=kL if L1=L2) where L is the resonantinductance and K is the coupling coefficient.If Rr<<RL the equation above is simplified to:

$\eta = {\frac{P_{load}}{P_{V\; 1}} = \frac{\omega^{2}M^{2}}{\left( {{R_{t}R_{L}} + {\omega^{2}M^{2}}} \right)}}$

For the particular case in which L1=L2=L, and assuming that η<<1 (in ourcase it is in the order of 0.001) the equation above leads to:

$k = \frac{\sqrt{\eta \; R_{L}R_{t}}}{\omega \; L}$

So, by knowing the equivalent real part of the impedance both for thetransmitter circuit and for the receiver circuit, and the ratio betweenthe power received and the power transmitted by the antennas (which inthis case it is dependent on the distance between the transmitter andthe receiver, on the antenna gains and on the conductivity of the tissuearound the receiver antenna), the value of K to simulate the systemcould be determined.

In reality it is quite difficult to estimate the Rt and RL both for thetransmitter and for the receiver because both circuits are not linear(the first one is not linear because there is a switch and the secondone because there is a diode rectifier).

In addition, since the impedance of the transmitter varies with theoutput voltage, the effect is that for the same k, the power received bythe receiver changes as well with the output voltage.

However typically it can be assumed that the output voltage remains atabout 5V during all the neural stimulation session. Therefore the systemhas been designed to have the highest efficiency around the outputvoltage range from 4V to 5V.

With reference now to the diagram of FIGS. 22-25, simulations of thesystem 100 will be now briefly described.

A large number of simulations have been performed with a large outputcapacitor set a given voltage.

A first simulation has been performed with an output voltage of 5 V. Thediagram of FIG. 22 shows the various dynamic power levels involved.

It can be noticed that the power used, after the initial transient dueto the settling of internal node voltages, by the source of thetransmitter is about 1 W, the one obtained at the transmitter antenna isin excess of 700 mW, the power received at the receiver antenna isalmost 2 mW (this assumes a path loss of 25.7 dB) and the power receivedby the load is about 1 mW.

The middle waveform of FIG. 12 represents, in dynamic form, the overallefficiency of the system 100 in percentage which is supposed to be atleast of 0.1% (1/1000). All this was done with a coupling coefficient ofabout 0.088 because the effective resistance of the transmitter and ofthe receiver circuit in their final form is quite high. For instance ithas been computed that for the receiver with no resistive load it is inthe order of 144Ω. This factor increases the coupling coefficient forthe same overall efficiency.

In the specific case described above the obtained voltage and currentwaveforms at the receiver antenna are shown in the diagram of FIG. 23and the current and voltage waveforms obtained at the transmitterantenna are illustrated in the diagram of FIG. 24.

It should be noted that this case is for a specific antenna impedance.The voltages and currents vary for different antenna impedances.

In addition, it is also important to verify and guarantee that thesystem 100 is able to charge the output capacitor C9 starting from aninitial condition of being totally discharged.

The diagram of FIG. 25 shows a simulation of that condition where theoutput capacitor value was reduced to 1 nF to prevent very longsimulation times.

It should be observed that for output voltages below 2V, although thepower received at the receiver antenna is in the order of 2 mW or more,the efficiency of the RF power receiver module is quite low. This isbecause, as explained earlier, the efficiency of the RF power receivermodule changes with its output voltage and it has been designed suchthat its efficiency is maximum at higher voltages (higher than 4V).

In this case the charge time was about 14 μs, which would imply that fora 1 μF output capacitor it would take something in the order of 15 ms,but again for different antenna impedances the charging times would varyas well. The simulations illustrated in FIG. 25 were performed with 10Ωof antenna resistance for the transmitter side and 5Ω of antennaresistance for the receiver side. These values are quite conservativeand it is evident that if the resistance values were smaller thecharging times would be shorter.

One of the initial objective of the present study was the ability tooperate the neural stimulation device without the need for an implantedbattery, but one of the possible future variants of the system is theuse of a super capacitor in place of the battery so as to allow thetherapy for a longer periods of time without the need to transmit alwaysthe RF power. The performed simulations showed that such system will besupported by the designed receiver without major modifications to thecircuit.

It should be also mentioned that during the system simulations it wasobserved that the impedance seen by the power amplifier of thetransmitter was slightly different from what simulated with thetransmitter only. In fact the overall efficiency was slightly lower dueto the fact that the ZVS conditions were not perfectly met any more.This observation has led to the need to increase the capacitor C1 ofFIG. 18 from 40 pF to 50 pF.

The electronic medical system according to the embodiments of thepresent disclosure, allows to overcome the disadvantages described abovewith reference to the prior art.

This is due mainly to the fact that the implantable medical device ofthe system of the present disclosure does not need the presence of animplanted battery as the system and/or the device of the prior art.

In fact, avoiding the presence of a battery, there are no problemsrelated to its presence, i.e. the need of its replacement by surgery,the impossibility of performing Magnetic Resonant Imaging (MRI) test,the presence of heavy metals and other potentially hazardous material,such as mercury, cadmium, nickel, and lithium, requiring extra care fordisposal avoiding leakage.

In addition, as expected, the overall efficiency of the system is quitelow (0.1%) and that is due to the nature of the far field RF powertransmission, however the system appears to be able to meet the initialrequirements of enabling the operation of a simple neural stimulationdevice implanted subcutaneously without the need for an implantedbattery for distance between the transmitter antenna and the receiverantenna in the 10 to 40 cm range at the frequency of 433.92 MHz.

A man skilled in the art may make several changes, adjustments andreplacements of elements with other functionality equivalent ones to theembodiments of the electronic medical system described above in order tomeet incidental needs, without departing from the scope of the followingclaims. Each of the features described as belonging to a possibleembodiment can be obtained independently of the other embodimentsdescribed.

1. An electronic medical system, comprising: an external RF powertransmitter configured to emit a first power signal via anelectromagnetic coupling, said RF power transmitter being configured toemit said first energy signal with a power no greater than 1 W; animplantable medical device comprising: at least one receiver antennaconfigured to receive said first energy signal via an electromagneticcoupling; an RF power receiver module operatively connected to the atleast one receiver antenna, the RF power module being configured toextract a second energy signal having a power of at least 1 mW, the RFpower receiver module being powered by said second energy signal, the RFpower receiver module being configured to generate a control signal; apower actuator module, operatively connected to the RF power receivermodule, powered by said second energy signal, the power actuator modulebeing configured to receive said control signal, the power actuatormodule being configured to deliver a medical treatment to at least atarget tissue of a patient on the basis of said control signal.
 2. Thesystem of claim 1, wherein the external RF power transmitter comprises aRF power transmitter module.
 3. The system of claim 1, wherein theexternal RF power transmitter comprises an energy storage element. 4.The system of claim 2, wherein the external RF power transmittercomprises a power limiter module operatively connected to the RF powertransmitter module, the power limiter module being configured to limitthe first energy signal to an instantaneous transmission power nogreater than 1 W.
 5. The system of claim 2, wherein the external RFpower transmitter comprises a first communication interface operativelyconnected to the RF power transmitter module, the first communicationinterface being configured to communicate data with the implantablemedical device via a wireless link.
 6. The system of claim 1, whereinthe external RF power transmitter further comprises a first programmablecontrol unit configured to manage the external RF power transmitter. 7.The system of claim 1, wherein the RF power transmitter module comprisea RF power amplifier, an impedance matching module, a resonant networkmodule and a transmitter antenna in cascade arrangement one another. 8.The system of claim 7, wherein the RF power amplifier is a Class-Eamplifier with Zero Voltage Switching.
 9. The system of claim 7, whereinthe RF power amplifier is configured to generate a second and a thirdharmonic components that are at least 70 dBc less than a carrierfrequency component.
 10. The system of claim 1, wherein the at least onereceiver antenna is of the subcutaneous type.
 11. The system of claim10, wherein the target tissue comprises a skin layer and a fat layer,the at least one receiver antenna is placed in the fat layer of thetarget tissue.
 12. The system of claim 11, wherein the at least onereceiver antenna is coated in a bio-compatible material.
 13. The systemof claim 12, wherein the bio-compatible material is a low electricalconductivity material.
 14. The system of claim 1, wherein the at leastone receiver antenna is printed on a flexible material.
 15. The systemof claim 1, wherein the at least one receiver antenna is anomnidirectional antenna.
 16. The system of claim 1, wherein the at leastone receiver antenna is a directional antenna.
 17. The system of claim1, wherein the at least one receiver antenna is a dipole antenna. 18.The system of claim 1, wherein the at least one receiver antenna is amonopole antenna.
 19. The system of claim 1, wherein the medicaltreatment is an electronic stimulation, the power actuator modulecomprising a pulse signal generator configured to apply electricalstimulation to the target tissue, controlled by means of the controlsignal, providing electrical stimulus to one or more electrodesconnected to the target tissue.
 20. The system of claim 1, wherein themedical treatment is the action of a medical substance, the poweractuator module comprising a pump, controlled by means of the controlsignal, to dispense the medical substance into the target tissue. 21.The system of claim 1, wherein the implantable medical device furthercomprises a second communication interface module operatively connectedto the RF power receiver module, said second communication interfacemodule being configured to communicate data with the external RF powertransmitter via a wireless link.
 22. The system of claim 21, wherein theimplantable medical device comprises a second programmable control unit,operatively connected to the RF power receiver module, configured tomanage the implantable medical device.
 23. The system of claim 22,wherein the implantable medical device further comprises a referencemodule operatively connected to both the RF power receiver module andthe second programmable control unit, the reference module beingconfigured to generate a reference voltage used by a pulse generatormodule within the RF power receiver module.
 25. The system of claim 1,wherein the implantable medical device comprises a RF front end module,an impedance matching network, a voltage rectifier, the power actuatormodule and a voltage protection and backscattering module.
 26. Thesystem of claim 25, wherein the voltage protection and backscatteringmodule is operatively connected to the at least one receiver antenna viathe RF front end module, the voltage protection and backscatteringmodule being operatively connected to the target tissue, the voltageprotection and backscattering module being configured to transmit to theexternal RF power transmitter feedback information received from thetarget tissue.
 27. The system of claim 1, wherein the external RF powertransmitter is configured to control the RF power transmission on thebasis of said feedback information.
 28. The system of claim 1, whereinthe external RF power transmitter may be worn by a patient.
 29. Thesystem of claim 1, wherein the external RF power module may be carriedout by a patient as a portable device.